This invention relates to the art of high resolution video displays such as scanning cathode ray tube display and to the use of such displays for simulating other lower resolution display forms for evaluation purposes.
It is common present-day practice to employ the cathode ray tube as an indicating display in the cockpit of an aircraft--for flight systems monitoring, weapon systems operation, navigation displays and for the presentation of external information obtained from, for example, a radar set or infrared camera. Although the art of aircraft cockpit displays has progressed significantly in response to the availability of denser and more capable electronic systems, the physical size, weight, fragility, voltage requirements, limited light output and other characteristics of the cathode ray tube have been restricting factors in the further improvement of such cockpit displays.
The evolution of matrix display devices such as the liquid crystal cell, the light emitting diode matrix, and even the incandescent lamp matrix (as is commonly employed in sports stadium scoreboards) has suggested such technologies as a possible replacement for the cathode ray tube in aircraft and other military electronic systems.
Some properties of these modern-day display devices are of course advantageous in aircraft and military systems use, notable among these properties are the small size, light weight, low operating voltage, immunity to large ambient light levels (at least for the reflective image types), long operating life and low power consumption. Most notable among the disadvantages of these modern-day display devices in their matrix or field of discrete elements nature. According to this nature, each information-bearing element is separated from adjacent information-bearing elements by an inactive display region which can occupy a significant portion of the total display area. In such displays the ratio of useful display area to total display area is often described in terms of an evaluating factor called the active area ratio for the display.
Other properties which require consideration in the application of a matrix display to a particular system include the density of the required display elements to adequately convey the anticipated information, the total number of display elements or image size required, the available dynamic signal range in the display elements and the response of the display elements to noise and other random signal modulation effects.
The liquid crystal cell in which an electric field causes the liquid crystal material to change from a transparent to a diffusing nature is one of the more promising matrix display devices for use in aircraft and other military systems. The liquid crystal cell, of course, does not generate light, but rather modifies the reflectance or transmission of incident light in response to an applied electric field. Properties and characteristics of liquid crystal displays are discussed in the published article "Liquid Crystal Matrix Displays", by B. J. Lechner, F. J. Marlow, E. E. O. Nester, and J. Tults published in the Proceedings of the IEEE Vol. 59, No. 11, November 1971, and also in the article "The Relative Merits of LED's and LCD's" written by L. A. Goodman, Proceedings of the SID, Vol. 16, No. 1, First Quarter, 1975. The contents of these two articles are hereby incorporated by reference into the present specification.
Before a liquid crystal display or other matrix display arrangement can be satisfactorily employed in either a replacement or new equipment environment where a high-resolution display such as a cathode ray tube might otherwise be used, careful consideration of human communicating characteristics is needed. An effective way for accomplishing these considerations is of course the fabrication of a sample display which is similar to the type contemplated for the equipment. Prior to the expense and time of constructing a working display, however, and while such a project is in the conceptual stages, it is frequently desirable to employ simulations of the contemplated display in order that the tradeoffs involved in an actual equipment design be evaluated quickly and at minimum cost. Such a simulation thereby allows the critical display parameters to be narrowed to a limited range of variation for making a final selection using actual working displays.
Heretofore, simulations of a matrix display have been achieved with photographic techniques including hand-laid opaque tape grid masks used in conjunction with actual photograph images for approximately evaluating the final display appearance. Clearly, such techniques involving tedious hand fabrication steps are both expensive and lacking in accuracy and flexibility. Simulations of this type are additionally somewhat optimistic in their presentation since the underlying photograph can include gray level information which may not be available or may be modified in density by the contemplated matrix display elements. The availability of computer and image processing techniques offers a convenient improvement over these prior art simulation techniques and allows the desired simulation to be accomplished using flexible and readily-available cathode ray tube monitors.
The U.S. Patent art includes numerous examples of electronically-controlled display apparatus, including cathode ray tube displays used for conveying electronically generated images to a human observer and employing electronic processing of the image information to achieve a variety of display modifications. An example of electronic processing used to control a display image includes the patent of Daniel W. Somerville, U.S. Pat. No. 4,242,678, which concerns a character generator that provides characters of variable size by electronically magnifying a basic character image and employing shape codes at each point of the basic character for expanding the point information.
The Somerville patent is, however, concerned with generating pleasing character shapes in a variety of sizes and height to width aspect ratios, rather than the processing of image information to achieve a simulated matrix display.
Another example of the prior patent art in the image display area is the patent of John T. Keller et al. U.S. Pat. No. 4,223,353, which addresses the question of display persistence desirable in a medical diagnostic apparatus employed in nuclear medicine testing procedures. The Keller apparatus provides electronically-generated display persistence using digital circuitry and is capable of numerous shades of display gray level. The Keller apparatus is an improvement on a prior art persistence apparatus which employed the decay of a cathode ray tube phosphor as the persistence generating mechanism. In addition to the increased number of gray levels, the Keller apparatus accommodates a large dynamic range of signals by way of a logarithmic conversion and notably allows operator control of the image persistence. In the Keller apparatus, persistence is determined by the amplitude of digital signals stored in a memory with the stored information being modified in accordance with an operator-elected persistence. The Keller invention does not teach the electronic variation of image parameters relevant to the simulation of a matrix display, however.
Two of my own prior patents, U.S. Pat. No. 4,510,525, concerning an Anaglyphic Stereoscopic Image Apparatus and Method, and U.S. Pat. No. 4,591,998 concerning a Dynamic Bar Pattern Apparatus and Method, also teach the use of electronic processing to modify information subsequently displayed on a cathode ray tube device. These two patents moreover employ computer-oriented processing involving some of the same processing hardware as employed in a preferred embodiment of tne present invention. The purpose and nature of the processing employed in these two prior patents is, however, significantly different from that of the present invention. In the first of my prior patents, a three-color display is employed for conveying a stereoscopic image relating to the density of an original image, while in the second of my prior patents the subject is the generation of a moving grid of bar patterns as might be employed in psychological testing and training. The disclosure of my two prior patents is however hereby incorporated by reference into the present specification.